Manganese electrowinning process



Patented July 10, 1951 UNITED STATES ATENT OFFICE MANGANESE ELECTROWINNING PROCESS signor to Electro No Drawing. Application February 4, 1946, Serial No. 645,481

4 Claims. (Cl. 204-105) This invention relates to the electrowinning of manganese.

In the art to which this invention relates, manganese is plated or deposited on a cathode as a result of the passage of an electric current through an electrolyte containing a manganese salt in solution, from an anode to a cathode.

Insofar as the electrowinning process is concerned, a type of cell commonly employed includes a plurality of cathodes connected in parallel, each cathode being contained within a catholyte chamber constructed in part of a porous diaphragm which serves to effect separation of the catholyte liquid contained in the catholyte cham-v ber from the anolyte liquid. Any desired num ber of catholyte chambers may be employed, i. e., the catholyte chambers may be arranged side by side in a row separated from each other by a predetermined distance. The plurality of catholyte chambers may be enclosed within the walls of a cell in which the anolyte chamber is constituted by that portion of the cell not occupied by the catholyte chambers. In this particular type of arrangement, anodes are positioned between the catholyte chambers and connected in parallel; the anodes and cathodes collectively being connected in series and provided with-a source of direct current which is passed through the cell from the anodes to the cathodes. This is merely one type of cell described to illustrate a typical arrangement. The invention is not in the cell construction as will hereinfater be clearly apparent and any suitable type of cell may be employed.

In the operation of such cells, it is necessary to replenish the electrolyte to compensate for the metallic manganese which is deposited therefrom. For this purpose it has now become common practice to remove anolyte liquid (electrolyte which has been depleted in its concentration of manganese) and replenish the manganese content thereof, e. g., by dissolving manganese therein.

One common form of doing this is to use the anolyte as a medium for extracting or dissolving the soluble content of a conditioned manganese ore. In this operation the anolyte is suitably contacted with manganese ore or other source of manganese. Since such sources of manganese, e. g., manganese .ore, contain not only manganese but other metals and impurities, it is necessary to purify the extract or solution so obtained in order to get satisfactory operation of the process may be oxidized to the ferric condition, precipitated as an insoluble ferric compound, and removed by filtration or otherwise along with other elements which will precipitate with the iron. After this step other impurities, e. g., nickel and cobalt, may be removed by suitable treatment. Whatever process is used has as its objective removal from the solution of all impurities which may interfere with the operation of the process and the deposition of metallic manganese in a very pure form.

The invention is not directed to the purification process and the above description is given merely to supply background in order that the invention may be more clearly understood.

Assuming that a suitably pure solution has been obtained, for use as catholyte, the latter is commonly introduced continuously into the catholyte chamber or chambers and metallic manganese is deposited therefrom on the cathode by the action of the electric current. As a matter of practice the catholyte as introduced into the catholyte chambers may contain, for example, 25 to 50 grams of manganese per liter as manganous sulfate and about to grams of ammonium sulphate per liter, and may have a pH of about 7.0 to 7.5. As a result of the electrolytic changes occurring, the concentration of manganese decreases. There is a transfer of electrolyte from the catholyte to the anolyte chamber in which the pH is substantially lower than in the catholyte chamber. In other words, the catholyte is distinctly alkaline, and may have a pH of about 7.0 to 9.0, whereas the pH in the anolyte has a typical range of about 1.0 to 2.0, sulphuric acid being generated in the anolyte chamber as a result of electrolytic changes.

Notwithstanding the fact that the solutions employed may be highly purified and the quality of the manganese deposit eminently satisfactory, the current efiiciency may be so low as to make the operation impractical. This effect is not marked in plating cycles of two to three hours such as has been commonly employed by researchers but such a cycle is far too short for commercial production of manganese metal where cycles of 24 hours or more are necessary. As the time of the plating cycle increases, the deleterious effect of decreasing current efiiciency becomes more pronounced and militates against continuous production of metal.

The decreased current efficiency is due to the fact that a greater portion of the electrical energy is consumed in plating out hydrogen in place of manganese. An approximate measure of the current efficiency may be obtained by dividing the current consumed in plating the manganese by.

the sum total of the current consumed in plating out hydrogen plus that consumed in plating the manganese. The waste of current in plating hydrogen is discussed as to general electrochemical theory and practice in such texts as Mantells Industrial Electrochemistry published by Mo- Graw-I-Iill Book Company, Inc., New York, New York. It will, therefore, be appreciated that it is desirable to provide means to decrease the current wastefully consumed in plating hydrogen relative to that necessary for plating manganese, and thus increase current efficiency.

A principal object of the invention is to maintain high current efficiencies throughout commercial plating cycles, e. g., 24 to 32 hours or longer.

In accordance with the invention direct current is passed through a solution from an anode to a cathode having a surface submerged in said solution to plate metallic manganese on that surface. The solution contains, in addition to the manganous sulfate and ammonium sulfate normally employed, a concentration of thiourea which may vary within the range of about 0.005 to about 0.06 gram per liter. Within this range concentrations of about 0.015 to 0.030 gram per liter are typical or preferred. The thiourea can be added in any convenient manner. For example, it can be added to the catholyte in the catholyte feed tank to which purified solution for use as catholyte is delivered and from which catholyte is fed into the catholyte chambers of the cells.

Conditions such as current density, cell temperature, rate at which manganese is deposited from the solution, pH range of solution, etc., may be varied in accordance with the practice and knowledge of the art. For example, the current density may be from about 20 to about 60 amperes per square foot of cathode surface, cell temperature may vary from 30 to 45 (3., rate of stripping, i. e., removal of manganese from catholyte and depositing or plating it on the cathode surface may be from to 35 grams per liter. The pH of the catholyte in the catholyte chamber may vary from 7 to 9, the concentration of manganese as manganous sulfate from about 12 to about 18 grams per liter and that of the ammonium sulfate from about 100 to about 180 grams per liter.

By proceeding in accordance with the invention, current efiiciencies not lower than about 60 to 68 percent may be realized.

Having explained the invention generically and specifically, the principles of the invention will be defined in the claims with the understanding that those principles may be embodied in a number of specifically different forms without departing from those principles.

What is claimed is:

1. Process of treating a manganese sulfate-ammonium sulfate aqueous solution for use as catholyte in the electrowinning of manganese which comprises adding to said solution thiourea to provide in said solution a concentration of thiourea of about 0.005 to about 0.06 gram per liter of thiourea.

2. Process for the electrowinning of manganese which comprises passing a direct current through a manganese sulfate-ammonium sulfate solution from an anode to a cathode having a surface submerged in said solution to plate metallic manganese on said surface, said solution containing about 0.005 to about 0.06 gram per liter of thiourea.

3. In the process of the electrowinning of manganese using a cell containing a cathode having a cathode surface submerged in a catholyte in a catholyte chamber and an anode having an anode surface submerged in an anolyte in an anolyte chamber and in which metallic manganese is plated on said cathode surface by passing a direct electric current from said anode to said cathode, the improvement which comprises employing as catholyte an aqueous manganese sulfate-ammonium sulfate solution containing about 0.005 to about 0.06 gram per liter of thiourea.

4. In the process of the electrowinning of manganese using a cell containing a cathode having a cathode surface submerged in a catholyte in a catholyte chamber and an anode having an anode surface submerged in an anolyte in an anolyte chamber and in which metallic manganese is plated on said cathode surface by passing a direct electric current from said anode to said cathode, the improvement which comprises employing as catholyte an aqueous manganese-sulfate-ammonium sulfate solution containing about 0.005 to about 0.06 gram per liter of thiourea, employing a plating cycle of not less than about 24 hours, and obtaining a current efiiciency throughout said cycle of about to 68 per cent.

WILLIAM L. HAMMERQUIST.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,903,860 Gockel Apr. 18, 1933 2,080,483 Hull May 18, 1937 2,316,937 Dean Apr. 20, 1943 FOREIGN PATENTS Number Country Date 540,228 Great Britain Oct. 9, 1941 OTHER REFERENCES Hendricks: Metal Industry, January 8, 1943, pp. 2628. 

1. PROCESS OF TREATING A MANGANESE SULFATE-AMMONIUM SULFATE AQUEOUS SOLUTION FOR USE AS CATHOYLTE IN THE ELECTROWINNING OF MANGANESE WHICH COMPRISES ADDING TO SAID SOLUTION THIOUREA TO PROVIDE IN SAID SOLUTION A CONCENTRATION OF THIOUREA OF ABOUT 0.005 TO ABOUT 0.06 GRAM PER LITER OF THIOUREA. 